Google is testing a new online advertising network that would let merchants pay a fee only when an internet user performs a specific action, such as buying a product or registering for a service.

If successful, the so-called "cost per action" (CPA) network would extend the search engine company's range of advertising activities and reduce its reliance on the "cost per click" model that has been at the heart of its early success. CPA networks, also known as affiliate marketing networks, let merchants sign up independent websites to find customers.

The website owner is typically paid only when a customer actually makes a purchase, or when they perform some other pre-determined action such as filling in a form on the merchant's site with their personal details.

Already used by companies such as Amazon.com, affiliate networks are starting to spring up more widely on the internet.

Ebay launched a form of a CPA network of its own last week, offering to pay affiliate websites that carry its auction listings a share of the sales commission if the adverts result in a sale.

- (Financial Times service)